1. Field of the Invention
This invention relates to derivatives of N-(2,2,6,6-tetraalkyl-4-piperidinyl)-containing carboxylic acid hydrazides. These compounds are very efficient in the stabilization of polymeric systems which are subject to degradation upon exposure to heat and/or light. These compounds contain both a hindered amine light stabilizing group and an acid hydrazide or derivative thereof. The acid hydrazide derivative enhances the photooxidative stabilizing properties of the hindered amine groups and contributes thermooxidative stabilizing and metal complexing properties to the compounds.
2. Description of the Prior Art
Hindered amine light stabilizers bearing carboxylic acid hydrazide functionality (hereinafter HALS-hydrazides) and derivatives thereof are known. There are five examples in the literature where the hindered amine moiety and the hydrazide moiety (--C(.dbd.O)--NH--NH.sub.2) are present in the same molecule. ##STR1##
Derivatives of these HALS-hydrazides are disclosed in several patents. U.S. Pat. Nos. 4,145,512 and 4,178,279 teach the reaction of HALS-hydrazide groups with isocyanate groups of polyisocyanates of isocyanate prepolymers to obtain light stabilized polyurethanes. U.S. Pat. No. 4,336,183 discloses acyl derivatives of HALS-hydrazides. U.S. Pat. No. 4,824,884 discloses cyclic anhydride derivatives of the parent N-(2,2,6,6-tetraalkyl-4-piperidinyl)amic acid hydrazides (of U.S. patent application Ser. No. 310,408). These derivatives are also efficient heat and light stabilizers for polymeric systems but do not fall under the scope of this invention.
U.S. Pat. No. 4,396,735 discloses mixtures of hindered amine light stabilizers and heterocyclic acid hydrazides for stabilizing synthetic resin compositions. Such systems are described as synergistic, since the combination is better than the hindered amine alone, and the hydrazide alone is not a light stabilizer.
In addition to activity as a stabilizer, commercially useful stabilizer additives must have both excellent compatibility with and/or solubility in the polymeric substrates to be stabilized along with superior resistance to loss from the stabilized composition during processing and end-use application. Many stabilizer additives exhibit limited compatibility in certain substrates and excessive tendency to exude, sublime and/or volatilize during weathering or processing of the stabilized composition. A major problem often exists when use conditions require prolonged exposure to elevated temperatures. Therefore, several attempts have been made to increase the compatibility and reduce the volatility of such stabilizer additives in various resin systems by modifying their structures. While improvements have been noted over the years, experience has shown that state-of-the-art stabilizers do not exhibit the desired combination of properties in all resins. Continued evolution of new polymeric compositions guarantees the need for additional structural modifications on any potential heat and/or light stabilizer intended for use. The versatility of the HALS-hydrazides disclosed herein allows for adaptation of the stabilizer combination to suit such new compositions.
The novel HALS-hydrazides of the instant invention are reactive hydrazides, capable of forming typical hydrazide derivatives. They can react with a variety of functional groups to permit property adjustment (such as compatibility and volatility). By careful selection of the proper derivative, one can increase the compatibility of the novel compounds with various host resins to be stabilized. The novel derivatives have low volatility and are not readily lost from polymeric systems via volatilization, migration or extraction. For example they react with cyclic anhydrides with formation of imides or amic acids; esters or acid halides with formation of acyl hydrazides; ketones and aldehydes with formation of hydrazones; chloroformates with formation of semicarbazates; and isocyanates with formation of semicarbazides. The diacyl hydrazide function (formed by reaction of the hydrazide with an anhydride, ester or acid halide) is, known to be particularly resistant to thermal degradation and a particularly useful antioxidant function (U.S. Pat. No. 3,639,334).
Polymers such as polyolefins (e.g. polyethylene, polypropylene, etc.) styrenics (e.g. polystyrene, rubber modified polystyrene, ABS, MBS etc.), polyvinyl chloride, polycarbonates, polyesters, polyphenylene ethers and polyamides for example are subject to degradation and discoloration upon exposure to heat and/or light with consequent deterioration of their mechanical properties. Various stabilizers have been proposed to inhibit such deterioration. Hindered piperidine light stabilizers have found extensive use in the photostabilization of polyolefins. Prior to the present invention, the results obtained with the known hindered amine light stabilizers have not been fully satisfactory with all types of maunfactured articles, either from a stabilization, compatibility, volatility, extrudability or economic viewpoint or combinations thereof. Therefore, further improvement in the field of hindered amine light stabilizers is still desirable. The novel compounds of this invention address these shortcomings.
Hydrazides have been used to prevent deterioration of polyolefins by heat, oxidation or heavy metal contamination. Derivatives of hydrazides are also commercially available for use as polymer stabilizers. (See Encyclopedia of Polymer Science and Engineering, 2nd Ed. Vol. 2, pp 83-84).